A team of Dutch scientists led by Lourens van Dijk from Utrecht University have successfully developed 3D printed light traps that drastically improve efficiency of photovoltaic solar cells.
The structures were 3D printed, polished with acetone, coated in reflective silver layer and placed on a small organic solar cell to test the concept and with positive results: the electrical output of the cell was increased even up to 13%.
Light trapping is usually achieved by changing the angle at which light travels in the solar cell by having it refract through angled surfaces and by concentrating more light on a panel surface.
Light traps are not a new invention but this is the first time that 3D printing was used to improve the performance by placing the light traps externally on the surface of a cell while most previous research was done on internal structures or surface textures. By using rapid prototyping several different geometrical configurations could be tested including the square, hexagonal, and circular concentrators.
Tested light traps can also be scalable and used in arrays. In the research they used small organic solar cells but this technology could be implemented on standard size photovoltaic modules currently utilized in power generation systems. Since it is a externally mounted module, it is highly likely that the existing solar panels could be upgraded.
As seen on the scheme above the 3D printed trap “captures” the light that reflects internally several times and thereby produces more energy. Photovoltaic cell with no light trapping apparatus or structure may have an optical path length of one device thickness, while a solar cell with good light trapping may have an optical path length of 50, indicating that light bounces back and forth within the cell many times. More light, higher bounce rate and light path length equals in more electrical energy output.
Worlds solar power is growing at high rate and photovoltaic electricity sources are becoming more important than ever in providing power without fossil fuel burning. On such a large scale even a small increases in photovoltaic efficiency can provide huge global impacts both in environment protection and economics of power production by decreasing the cost.
Entire research was published in a paper authored by Lourens van Dijk, E.A. Pepijn Marcus, A. Jolt Oostra, Ruud E.I. Schropp, and Marcel Di Vece and is available under Creative Commons license. Full scientific article can be seen at:
… but if you don’t have the time here is the abstract:
After our recent demonstration of a 3D-printed external light trap on a small solar cell, we now consider its potential for large solar panels. An external light trap consists of a parabolic concentrator and a spacer that redirects the photons that are reflected by the solar cell back towards the solar cell. These retro-reflections enable higher absorptance and improved power conversion efficiency. Scaling a single external light trap such that it covers a large solar panel has disadvantages in terms of height and cost of the external light trap. These disadvantages can be overcome by deploying an array of concentrators as the top part of the external light trap. We present an optimization study of concentrator arrays for external light trapping. We fabricated 3D-printed external light traps with a square, hexagonal and circular compound parabolic concentrator to test their suitability for concentrator arrays. The 3D-printed traps were placed on top of an organic solar cell which resulted in a significant enhancement of the external quantum efficiency. The required transmittance of these concentrator arrays is calculated as a function of the parameters of both the concentrator and the solar cell. We compare the theoretical and experimentally determined optical performance of the different concentrators. Finally, the prospects of external light trapping are analyzed and we give guidelines for improvements of the external light trap design.
The conclusion of the research paper is:
We demonstrated that external light trapping is of interest for all solar cells as its effectiveness does not depend on the refractive index or texture of the solar cell and it is easy to apply. As the device is an add-on it guarantees that there is no negative impact on the electrical properties of the solar cell. We proposed several possible designs for an array of concentrators that can be integrated in an external light trap that covers a large solar cell area. The use of 3D-printed light traps with a square, hexagonal and circular parabolic concentrators resulted in a significantly improved EQE of an organic solar cell. Excellent agreement was found between the fit based on our model and the experimental data, which shows the predictive power of the model. Moreover, an effective path length enhancement factor larger than 2 is observed while the EQE improved by up to 69%rel, corresponding to an increase of the short circuit current of 13%. This indicates that external light trapping is an interesting alternative or supplement for internal light trapping.
If you are more deeply interested in general science behind light trapping for solar cells you can watch this presentation from Stanford University:
This development is another great example how 3D printing can be used to make existing technologies more efficient and improve the environment with clean energy production.